The invention relates to a process for attaining a yieldable connection between a metallic rod-shaped body and a holding means through which it passes including bodies guided therein and projecting into its open cross-section.
In many cases it is desirable for load bearing constructions to have high yieldability whilst retaining their load-bearing ability. Thus, in tunelling, earth-moving and mining, load bearing constructions are desired which can partake in the deformations of the overburden and of earth masses without breakage. Rock bolts, for example, are so designed that the overburden bears onto yieldable constructions. The desired yieldability may for example be attained by a connecting member on the anchoring rod which slides along the latter due to the load of the overburden or, e.g. in that between the overburden and a fixed point, along the anchor, a crushing body is provided. Such anchors may be relaxed or pretensioned.
In tunnelling and mining tubbing constructions of steel or steel reinforced concrete have been moreover proposed which in order to increase the deformability of the roof support, comprise crushing zones between the tubbings. Whenever the overburden moves towards the cavity, the crushing zones between the tubbings are compressed. Other roof support means such as arches, props and the like may also be equipped with crushing constructions in order to retain the supporting action even in the event of overburden deformations.
The aforesaid yieldable constructions are employed in mining and tunnelling also as a safeguard against rock falls and rock bursts. The kinetic energy of the rock falls or rock bursts being rendered harmless by being absorbed by the deformation energy of the yieldable construction.
The same purpose - the conversion of kinetic energy into deformation energy - is served by yieldable constructions in traffic engineering, e.g. in the form of yieldable retaining means for persons in vehicles, crushing zones in vehicles or in the form of catching constructions for vehicles, e.g. retention railings, retention nets and buffer blocks having predetermined yieldabilities. Similar yieldable constructions are employed as protection against avalanches, rock falls and other falling or flying objects.
For obtaining the desired yieldability, anchor heads have become known in the case of anchors which can slide along an anchor rod when subjected to the load of the over burden when subjected to rock pressure.
This may be attained by an anchor head designed as a drawing die. In the event of sliding between the anchor rod and the anchor head, the anchor rod is drawn through the anchor head designed as a drawing die; the anchor rod is thereby subjected to a reduction in cross-section. In this context a number of different constructions are possible. For example, anchors comprising an anchor rod composed of a comparatively thin rod member onto which the anchor head in the form of a drawing die has been pushed and a relatively thicker rod member which on sliding of the anchor head along the anchor rod suffers a reduction in cross-section. The thicker rod member can also be in the form of a threaded rod, such that the thread, as the rod is drawn through the drawing die, is stripped.
In the case of anchors it is also known to have anchor heads which are slidable on the anchor rod, in which the anchor rod and the anchor head are interengaging bodies between which a space of tapering configuration is provided. This is filled with a particulate material which is subjected to pressure in the direction of taper of the space. If the anchor rod is moved in relation to the anchor head in the direction of taper of the space, the particulate filling material, e.g. spheres, is pressed into the material of the anchor rod or of the anchor head and of the anchor rod. Sliding is therefore possible only with force. The described construction comprising an anchor head and rod represents a forced transmission device in which forces are transmitted preferentially in the longitudinal direction of the rod, deformation work being exercised during the sliding movement between the anchor head and the rod.
From DE-OS No. 2 511 706 a yielding anchor is known which comprises a tube anchored in a drilled hole in which tube the anchor rod slides when a force is exercised. The transfer of forces between the rod and the tube proceeds by way of a bolt which is mounted vertically to the axis of the rod on the borehole side of the anchor rod end. These bolts engage into a lining adhering to the tube interior and cause the lining to be stripped in the event of the anchor rod sliding in the tube.
Yieldable connections are subjected to requirements which depend on their intended use. The object here desired is a yie1dable connection having the following characterstics: It should be able to transmit high forces, e.g. 1 000 kN, even over major sliding distances of e.g. 30 cm, is to attain a full load bearing ability even after a short sliding distance and to retain this load bearing ability following further displacement. It is to be applicable to ribbed or smooth solid or hollow rods and is to be suitable for rods which are either subjected to traction or to compression. In spite of small dimensions it is to be able to transmit high forces, must be robust and as little as possible affected by external factors such as temperature, moisture or dirt. Moreover, it is to be of simple construction and should be capable of being manufactured as economically as possible.
The known constructions attain these objects only partly, or inadequately.
The aforementioned anchors, in which a yieldability is attained in that the anchor rod under load is drawn through an anchor head designed as a drawing die, require anchor rods which, because of their special configuration, and high degree of dimensional accuracy, are expensive. Moreover these constructions are virtually only suitable for rods subjected to tensile forces.
The aforementioned yieldable anchors which comprise an inner lining in a tube anchored in a borehole, and which lining on sliding of the anchor rod in the tube is stripped by bolt formations, are expensive in design and of very limited load-bearing ability.
The aforedescribed anchor heads in which the forces acting onto the anchor rods are transmitted by way of a particulate filling material, and which can be mounted on non-machined ribbed anchor rods, do not meet the requirements because they attain their full load-bearing ability after only a short sliding movement.